We have continued our studies of chromatin structure in the neighborhood of expressed genes. The globin gene family in chicken erythroid cells serves as a model system in which it is possible to study the mechanisms associated with regulation of the individual members of the family during erythroid development. We have extended our studies of the way in which hypersensitive sites are generated in the chicken beta globin enhancer and in constructions carrying various parts of the enhancer. A new assay allows separation of cells in which the enhancer is transcriptionally active from those in which it is not, so that the role of chromatin structure in switching can be explored. We have also exploited our earlier analysis of the binding of the erythroid regulatory factor GATA-1 carboxy-terminal zinc finger to DNA to study the way in which GATA-1 interacts with nucleosome core particles. Separate studies of the interactions of GATA-1 with target DNA have revealed an important role for the amino-terminal finger in binding to special sites found upstream of all the known GATA-1 genes. We have also studied the properties of the regulatory factor called the GAGA protein, which is implicated in disruption of chromatin structure. We find that the single zinc finger of this protein confers strong specific binding on the protein, mediated by a nearby sequence of basic residues. This is the first zinc finger of the class containing two cysteines and two histidines shown to bind as a single finger, and suggests that many other known proteins of this type might be studied for DNA binding properties. We have also continued studies of the way in which RNA polymerase transcribes through chromatin templates. We have extended our model system to isolate complexes in which the polymerase is arrested at the half way point on the template. It is immediately after this that the histone octamer transfers behind the nucleosome. The structure of this intermediate is being studied.